Predicting the speed at which black-grass is likely to emerge, along with the population pressure, could help with agronomy decisions including drilling date, crop choice and autumn herbicide options.
That is according to Syngenta technical manager Georgina Wood, who says results from a complex matrix of five years’ establishment system trials on the Syngenta Barton Black-grass Innovation Centre, Cambridge, have revealed a clear correlation between seed movement in the soil bank and long-term black-grass management.
She says: “If you know where most shed seed has been moved to in the soil profile each year, you can begin to calculate how much is likely to appear this season and, equally importantly, when it will emerge.”
The length of time seed has been in the soil will determine its viability to grow, along with its position in the seedbank, dictating emergence timing.
Seed within 2cm of the soil surface could see nearly 90% emergence within seven days of germination, for example, however seed at about 6cm is more likely to result in less than 60% germination and take 12 days to emerge.
Emergence “Where seed is coming from 8cm, at the bottom of a non-inversion tillage system, for example, emergence could be less than 10% and take more than 17 days to come up.
Seed buried down below 10cm with the plough has shown little or no emergence.”
Based on the research results, Syngenta has created an online cultivation insight tool, which enables growers to model where seed is likely to have moved in successive seasons under different establishment systems.
The implication is that where black-grass seedlings are coming from depth, there could be lower weed pressure in terms of total numbers, but the flush will appear over a protracted length of time.
“In those scenarios delaying drilling, to provide more time to kill off the weed flush, is going to be even more important.
Furthermore, it also impacts on herbicide strategy, where the residual activity of any pre-emergence application is going to be more robustly tested.
That puts the onus on application to be as effective as possible, as well as the potential for a sequenced Defy-based herbicide approach.”
Increasing seed rate and growing a more vigorous hybrid barley to outcompete later emerging black-grass could prove especially effective in these situations, Ms Wood says.
She adds growers also need to factor in the dormancy level of black-grass seed shed in any particular season to predict potential timing and threats to the establishing crop.
“Warm, dry conditions during black-grass seed setting indicates potentially low dormancy.
However, cool, wet conditions, such as experienced this season, suggest it is more likely to be a high dormancy autumn.
That could mean seed will germinate and emerge over a more protracted period – requiring agronomy decisions to be tailored accordingly.”
Strategy Trials at the Barton unit have historically shown that in a season with prolonged weed emergence, a sequenced approach to autumn herbicide strategy can provide a useful increase in control of around 5% compared to pre-emergence alone.
“That does have to be balanced against the risk of not being able to physically get the second application on if weather or soil conditions are difficult, compared to the assurance of a stacked pre-emergence strategy,” she adds.